Embodiments of the invention relate generally to fin-shaped field effect transistors (FinFETs) which may include silicon germanium (SiGe) stressors. More specifically, embodiments of the invention include a method of forming a FinFET with a SiGe stressor and a resulting FinFET structure.
In integrated circuit (IC) structures, a transistor is a critical component used to implement digital circuitry designs. Generally, a transistor includes three electrical terminals: a source, a drain, and a gate. By applying different voltages to the gate terminal, the flow of electric current from the source to the drain can be enabled or disabled. A common type of transistor is a metal oxide field effect transistor (MOSFET). One type of MOSFET design is known as a “FinFET,” typically built upon a semiconductor-on-insulator (SOI) layer and buried insulator layer. A FinFET can be composed of a semiconductor structure etched into a “fin” shaped body, with one side of the fin acting as a source terminal and the other side of the fin acting as a drain terminal. A gate structure, typically composed of polysilicon and/or a metal, can be formed around one or more of the semiconductor fins. By applying a voltage to the gate structure, an electrically conductive channel can be created between the source and drain terminals of each fin in contact with the gate.
To enhance the operation of an IC, mechanical stress may be applied to the transistors of the circuit. For example, the operation of a p-type MOSFET is enhanced if a compressive stress is applied to its channel, while the operation of an n-type MOSFET is enhanced if a tensile stress is applied to its channel. To apply mechanical stress to an IC component composed of single-crystal semiconductor (e.g., the fins of a FinFET), a “stressor” material can be introduced to the component. Silicon germanium (SiGe), a conventional stressor used in MOSFETs and sometimes used in a FinFET, can be introduced, for example, by creating a recess within source and drain regions of the transistor and growing epitaxial silicon germanium (SiGe) therein. This conventional process of introducing a stressor material may be limited by the amount of semiconductor material (e.g., silicon) available in the recessed semiconductor fin. The various crystal growth conditions of SiGe, in some cases, can also create a faceted epitaxy at the bottom of the recess within the fin, which will prevent the application of strain to the semiconductor fin.